Background. Carers of patients with clinical dementia have increased rates of depressive illness but the biological mechanisms by which the stress of caring can lead to mood disorders is not well understood.

Methods. We recruited 30 full-time carers of patients with dementia and 28 age and gender-matched controls. None of the subjects were suffering from a significant depressive disorder. We measured salivary cortisol at four time points throughout a single day and also took a single fasting morning blood sample for plasma tryptophan.

Results. Salivary cortisol levels were significantly higher in carers than controls at 12.00 h and 22.00 h. Plasma total tryptophan but not free tryptophan levels were significantly lower in carers.

Conclusions. The changes found in these non-depressed carers were essentially similar to those in patients with major depression. We suggest that increased cortisol secretion and lowered tryptophan availability increase the risk of mood disorders in carers.